JPH05140765A - Treatment for surface of copper foil for printed circuit - Google Patents

Abstract

PURPOSE:To obtain a treating method by which the thermal oxidation resistance on the bright face of copper foil increases so that decoloration will not occur even under heating at a temp. higher than heretofore and solder wettability, resist adhesion or the like are not lowered. CONSTITUTION:On the bright face of copper foil for a printed circuit, a Zn-Ni alloy layer having a compsn. of 50 to 97wt.% Zn and 3 to 50wt.% Ni is formed by 100 to 500mug/dm<2> coating quantity, and after that, Cr rust-proofing treatment is executed. The Cr rust-proofing treatment contains single film treatment of chromium oxide and/or mixed film treatment of chromium oxide and zinc and/or zinc oxide. Treatment for forming one or >= two kinds of single metallic layer or allay layers selected from Cu, Cr, Ni, Fe, Co and Zn can be executed on the roughened face of the steel foil. Decoloration does not occur even under high temp. conditions of 240 deg.CX30min or 270 deg.CX10min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a printed circuit copper foil, and more particularly to a thermal oxidation resistance (not discoloration due to thermal history applied when manufacturing a printed circuit board or the like). The present invention relates to a method for treating a glossy surface of a copper foil for a printed circuit, which comprises forming a Zn—Ni alloy layer before forming a Cr-based rust preventive layer in order to improve

[0002]

2. Description of the Related Art Generally, a printed circuit copper foil is laminated and adhered to a base material such as a synthetic resin under high temperature and high pressure, and after printing a necessary circuit to form a target circuit, an unnecessary portion is removed. An etching process is performed. Finally, the required components are soldered together to form various printed circuit boards for electronic devices. Quality requirements for copper foil for printed wiring boards differ between the surface (roughened surface) bonded to the resin substrate and the non-bonded surface (glossy surface).

The requirements for the roughened surface are mainly that there is no oxidative discoloration during storage, and that the peeling strength from the substrate is sufficient even after high temperature heating, wet treatment, soldering, chemical treatment, etc. For example, there is no so-called laminated stain that occurs after lamination with a substrate or etching.

On the other hand, the glossy surface has a good appearance, no oxidative discoloration during storage, good solder wettability, no oxidative discoloration when heated at high temperature, and good adhesion to the resist. Something is required.

In order to meet such demands, many treatment methods have been proposed for various purposes with respect to the roughened surface and the glossy surface of the copper foil for printed wiring board. In particular, paying attention to the anticorrosion treatment of the copper foil, the applicant of the present invention, as one of the useful basic antirust methods, formed a zinc film on the glossy surface of the copper foil in Japanese Patent Publication No. 61-33908, and subsequently, A method of forming a chromium anticorrosive layer by a chromium oxide film was proposed. Also,
Regarding the chrome rust preventive layer itself, a mixed film treatment of chromium oxide and zinc and / or zinc oxide by electrolytic zinc / chromium treatment has been proposed (Japanese Patent Publication No. 58-7077) and many results have been achieved. .. Further, in JP-A-2-294490, for the purpose of preventing the generation of black spots under a high temperature and high humidity condition for a long period of time, a chromium oxide film is formed by immersion chromate treatment, and then chromium is treated by electrolytic zinc / chromium treatment. It is disclosed to form a mixed film of oxide and zinc and / or zinc oxide.

[0006]

By the way, with respect to the thermal oxidation resistance of the glossy surface of the copper foil, demands are becoming stricter year by year. One is a new manufacturing method that has never existed before (two-layer flex: a polyimide varnish is directly applied on a copper foil to form a flexible substrate, which has a two-layer structure of a polyimide layer and a copper foil layer. This is because the copper foil is exposed to higher temperatures than before with the advent of new resins with high heat resistance. In addition, even in the conventional laminating method, there is a tendency to perform the heat treatment in the atmosphere from the nitrogen atmosphere to reduce the cost of the laminating and curing steps. From this point as well, the thermal oxidation resistance of the glossy surface of the copper foil is seen. Improvement has come to be required.
With the current method of zinc plating + chromate treatment, the thermal oxidation resistance is maintained only for, for example, about 200 ° C. × 30 minutes, and 240 ° C. × 30 minutes or 270 ° C. × 10 which will be required in the future.
It discolors under high temperature conditions for a minute. Therefore, in order to meet the future demand for copper foil for printed circuits, 240 ° C x 3
It is necessary to ensure a higher level of thermal oxidation resistance that does not discolor even under higher temperature conditions such as 0 minutes or 270 ° C. × 10 minutes. In addition, it should not impair other properties required for the glossy surface, such as solder wettability and resist adhesion.

The object of the present invention is to provide conventional zinc plating +
In the chromate treatment method, the thermal oxidation resistance of the glossy surface of the copper foil is increased so as not to cause discoloration with respect to the thermal history expected in future printed circuit board manufacturing, and other properties such as solder wettability and resist adhesion are impaired. It is to develop a unique processing method.

[0008]

The present inventors have found that the above problems can be solved by forming a very thin Zn-Ni alloy film in place of the conventional zinc single plating. Zn-Ni alloy plating itself is used, for example, to improve heat resistance and corrosion resistance in automobile engine rooms and body steel sheets, but the environmental conditions of use are completely different between plating with such a general structural material and printed circuit copper foil. ,
It can be said that this is a completely different technology. As an application of Zn-Ni alloy plating to copper foil, increase in peel strength, prevention of migration, to the roughened surface of the copper foil, not to the glossy surface,
There is an attempt to perform Zn-Ni alloy plating for the purpose of improving hydrochloric acid resistance and heat resistance (see, for example, JP-A-61-111).
0794, JP-A-63-89698, JP-B-2-5
No. 1272), the requirements required as described above are completely different between the glossy surface and the roughened surface. Particularly, in the above-mentioned known method, the plating thickness is too thick, and there is a problem in appearance as a copper foil for a printed circuit board. However, it is not at a level that can be used. Therefore, the above-mentioned method was carried out, and a diligent study was carried out so that a plating film having a thickness of about 3 μm could be applied to a region of several tens to several hundreds of Å as a printed circuit board. As a result, it was discovered for the first time that the thermal oxidation resistance of the glossy surface is improved by applying a very thin Zn-Ni alloy coating to the glossy surface.

Based on this finding, the present invention provides a Zn-Ni alloy layer comprising 50 to 97% by weight Zn and 3 to 50% by weight Ni on the shiny side of a printed circuit copper foil in an amount of 100 to 500 μm.
The present invention provides a surface treatment method for a copper foil for a printed circuit, which is characterized in that it is formed with an adhesion amount of g / dm ² and then a Cr-based rust preventive layer is formed on the Zn—Ni alloy layer. In this case, on the roughened surface (non-glossy surface) of the copper foil, Cu, Cr, N
It is preferable to perform a treat treatment for forming a single metal layer or an alloy layer of one or more selected from i, Fe, Co and Zn. To further improve weather resistance, C
It is preferable that the r-type rust preventive layer is formed of a chromium oxide film by immersion chromate treatment or electrolytic chromate treatment and / or a mixed film of chromium oxide and zinc and / or zinc oxide by electrolytic zinc / chromium treatment.

[0010]

Function: A Zn-Ni alloy film is formed on the glossy surface of the printed circuit copper foil. The Zn-Ni alloy treatment is preferably Zn-
Using a Ni electrolytic plating bath, a Zn-Ni alloy layer having a composition of 50 to 97 wt% Zn and 3 to 50 wt% Ni was used.
It is carried out so as to form a very thin film with an adhesion amount of 0 to 500 μg / dm ² . If the amount of Ni is less than 3% by weight, the required improvement in thermal oxidation resistance cannot be obtained. On the other hand, when the amount of Ni exceeds 50% by weight, the solder wettability deteriorates and the thermal oxidation resistance also deteriorates. The amount of Zn-Ni alloy layer deposited is 100 μg
If it is less than / dm ² , the improvement in thermal oxidation resistance cannot be obtained. On the other hand, when it exceeds 500 μg / dm ² , conductivity is deteriorated due to diffusion of Zn and the like. The Zn-Ni alloy layer enhances the thermal oxidation resistance of the glossy surface of the copper foil and does not impair other properties such as solder wettability and resist adhesion.

[0011]

EXAMPLES The copper foil used in the present invention may be either electrolytic copper foil or rolled copper foil. Although the present invention is concerned with the glossy surface of the copper foil, the roughened surface of the copper foil will be described for reference. Usually, on the surface of the copper foil that is bonded to the resin substrate, that is, the roughened surface, for the purpose of improving the peeling strength of the copper foil after lamination, the surface of the copper foil after degreasing, for example, is made of copper Roughening treatment is carried out for performing electrodeposition of the shape. Such copper hump-like electrodeposition is easily brought about by so-called burn electrodeposition. Normal copper plating or the like may be performed as a pretreatment before roughening, and normal copper plating or the like may be performed as a finishing treatment after roughening.

The following conditions can be adopted as an example of the copper roughening treatment. Copper roughening treatment Cu: 10 to 25 g / l H ₂ SO ₄ : 20 to 100 g / l Temperature: 20 to 40 ° C. D _k : 30 to 70 A / dm ² hours: 1 to 5 seconds

After the roughening treatment, Cu, Cr, N is formed on the roughened surface.
It is preferable to perform a treat treatment for forming a single metal layer or an alloy layer of one or more selected from i, Fe, Co and Zn. As an example of alloy plating, Cu-
Ni, Cu-Co, Cu-Ni-Co, Cu-Zn and the like can be mentioned (for details, see Japanese Patent Publication No. 56-902).
No. 8, JP-A-54-13971, JP-A-2-2928.
95, JP-A-2-292894, JP-B-51-35.
711, Japanese Examined Patent Publication No. 54-6701, etc.).
Such treat treatments serve as a determinant and barrier to the final properties of the copper foil.

According to the present invention, the roughened surface of the copper foil is subjected to the Zn-Ni alloy treatment on the shiny side with or without the treatment. Zn-Ni alloy treatment is preferably 50-97 wt% using a Zn-Ni electroplating bath
A Zn-Ni alloy layer containing Zn and 3 to 50% by weight of Ni is formed to a very thin thickness with a deposition amount of 100 to 500 μg / dm ² . If the amount of Ni is less than 3% by weight, the required improvement in thermal oxidation resistance cannot be obtained. On the other hand, when the amount of Ni exceeds 50% by weight, the solder wettability deteriorates and the thermal oxidation resistance also deteriorates. The amount of Zn-Ni alloy layer deposited is 100 μg
If it is less than / dm ² , the improvement in thermal oxidation resistance cannot be obtained. On the other hand, when it exceeds 500 μg / dm ² , conductivity is deteriorated due to diffusion of Zn and the like. Further, it is expected that the solder wettability will be deteriorated in the process in which no flux is used. The adhered amount is made thin as described above so that the appearance is not so different from the copper color.

The composition and conditions of the Zn-Ni plating bath are as follows: Zn: 5 to 50 g / l Ni: 5 to 50 g / l pH: 2.5 to 4 Temperature: 30 to 60 ° C. Current density: 0.5-5 A / dm ² Plating time: 1-10 seconds

In addition to the Zn-Ni alloy, the same effect can be obtained with the Zn-Co alloy.

After washing with water, a rust preventive treatment for forming a Cr rust preventive layer on the Zn-Ni alloy layer is carried out. The Cr-based rust preventive layer is a rust preventive layer mainly composed of chromium oxide formed by a single film treatment of chromium oxide or a mixed film treatment of chromium oxide with zinc and / or zinc oxide. Say a layer. For the single film treatment of chromium oxide, either immersion chromate or electrolytic chromate may be used. When weather resistance is required, electrolytic chromate is preferable. The conditions of immersion chromate or electrolytic chromate follow the conditions established in the art. For example, examples of conditions for immersion chromate treatment and electrolytic chromate treatment are as follows: (A) Immersion chromate treatment K ₂ Cr ₂ O ₇ : 0.5 to 1.5 g / l pH: 1.4 to 2.4 Temperature : 20 to 60 ° C Time: 3 to 10 seconds (B) Electrolytic chromate treatment K ₂ Cr ₂ O ₇ (Na ₂ Cr ₂ O ₇ or CrO ₃ ): 2 to 10 g / l NaOH or KOH: 10 to 50 g / l pH : 7 to 13 Bath temperature: 20 to 80 ° C Current density: 0.05 to 5 A / dm ² hours: 5 to 30 seconds Anode: Pt-Ti plate, stainless steel plate, etc.

The treatment of a mixture of chromium oxide and zinc / zinc oxide is carried out by electroplating zinc or zinc oxide and chromium oxide using a plating bath containing zinc salt or zinc oxide and chromate. This is a treatment for coating the rust preventive layer of the zinc-chromium group mixture, which is called electrolytic zinc-chromium treatment. The plating bath is typically K ₂ Cr ₂ O ₇ , N
A mixed aqueous solution of at least one dichromate such as a ₂ Cr ₂ O ₇ or CrO ₃ and at least one water-soluble zinc salt such as ZnO or ZnSO ₄ .7H ₂ O and an alkali hydroxide is used. .. Typical plating bath compositions and examples of electrolysis conditions are as follows: (C) Electrolytic zinc / chromium treatment K ₂ Cr ₂ O ₇ (Na ₂ Cr ₂ O ₇ or CrO ₃ ): 2 to 10 g / l NaOH or KOH: 10 to 50 g / l ZnO or _{ZnSO 4 · 7H 2 O: 0.05~10g} / l pH: 7~13 bath temperature: 20 to 80 ° C. current density: 0.05 to 5 A / dm ² Time: 5 ~ 30 seconds Anode: Pt-Ti plate, stainless steel plate, etc. Chromium oxide requires a chromium amount of 15 µg / dm ² or more and zinc has a coating amount of 30 µg / dm ² or more. The rough surface side and the glossy surface side may have different thicknesses. Such rust prevention methods are disclosed in Japanese Patent Publications Sho 58-7077, 61-33908,
62-14040 and the like. A combination of chromium oxide alone and a mixture of chromium oxide and zinc / zinc oxide is also effective.

The copper foil obtained after washing and drying with water is, for example, 200 ° C. by the conventional method of zinc plating + chromate treatment.
It had a heat-resistant oxidation resistance of only about × 30 minutes, while 2
It has thermal oxidation resistance that does not discolor even under high temperature conditions of 40 ° C x 30 minutes or 270 ° C x 10 minutes. Moreover, it does not impair other properties such as solder wettability and resist adhesion.

Finally, if necessary, a silane treatment for applying a silane coupling agent to at least the roughened surface of the rust preventive layer is performed for the main purpose of improving the adhesive force between the copper foil and the resin substrate. The coating method may be spraying of a silane coupling agent solution, coating with a coater, dipping, pouring, or the like. For example, Japanese Examined Patent Publication No. 60-15654 discloses that the adhesion between the copper foil and the resin substrate is improved by subjecting the rough surface side of the copper foil to a chromate treatment and then a silane coupling agent treatment. .. For details, refer to this.

Thereafter, if necessary, an annealing treatment may be performed for the purpose of improving the ductility of the copper foil.

(Examples and Comparative Examples) A rolled copper foil was provided with (1)
Zn-Ni alloy or Zn single plating → washing → (2) C
r Surface treatment was applied in the order of immersion plating → washing with water → drying (glossy surface). On the other hand, the roughened surface was subjected to Cu-Ni treatment after copper roughening, and then Cr immersion plating. (1) Zn-
Ni alloy plating and (2) Cr immersion plating and (3)
The conditions of Cu-Ni alloy plating were as follows: (1) Zn-Ni (or Zn alone) alloy plating Zn: 20 g / l Ni: zero or 10 g / l pH: 3 Temperature: 40 ° C Current density: 2A / dm ² plating time: 1.5 seconds (2) Cr dipping plating K ₂ Cr ₂ O ₇ : 1 g / l pH: 2.0 Temperature: 40 ° C. Time: 5 seconds (3) Cu-Ni alloy plating Cu: 5 -10g / l Ni: 10-20g / l pH: 1-4 Temperature: 20-40 ° C Current density: 10-30A / dm ² Plating time: 2-5 seconds

The glossy surface of the obtained product was tested for surface adhesion, baking test and solder wettability. In the surface analysis, the roughened surface was pressed with a substrate material such as FR-4 for masking, immersed in an acid to dissolve Zn and Ni only on the glossy surface, and analyzed by an atomic absorption method. Baking test is copper foil 600mm width x 100m
After the m-length test piece was put into a predetermined oven and taken out, the presence or absence of discoloration on the glossy surface was confirmed (judgment criterion 0 = no discoloration. × = discoloration). Regarding solder wettability, the pressed board was vertically dipped in a solder bath using JS64 manufactured by Tamura Kaken Co., Ltd. as a flux, and the wetting angle of the solder sucked along the board surface was obtained. The smaller the angle, the better the solder wettability.

The test results are as follows: No. Zn Ni adhesion amount (μg / dm ² ) Baking test Solder wettability (g / l) (g / l) Zn Ni Cr 240 ^o C / 30min 270 ^o C / 30min Wetting angle Wetting 1 20 0 230 --26 × × 39.5 100% 2 20 10 230 28 26 ○ ○ 42.7 100%

From the above test results, the following matters are confirmed. About 11% of Ni was contained in the coating of the Zn-Ni plated product with respect to the Zn plated product. The glossy surface thermal oxidation resistance is very good, while the Zn-plated product discolored, whereas the Zn-Ni plated product did not discolor. There is almost no difference in solder wetting and there is no problem because the wetting is 100%.

[0026]

EFFECTS OF THE INVENTION The product of the present invention, which has improved thermal oxidation resistance as compared with the conventional zinc plating + chromate treatment method product, prevents discoloration of the copper foil glossy surface against future heat history at the time of printed circuit board manufacturing, Moreover, other characteristics such as solder wettability and resist adhesiveness are not impaired, and future demands for copper foils for printed circuit boards can be met.

Claims (3)

[Claims] 1. A Zn-Ni alloy layer comprising 50 to 97% by weight Zn and 3 to 50% by weight Ni is formed on the shiny side of a copper foil for a printed circuit at an adhesion amount of 100 to 500 μg / dm ² .
Thereafter, a Cr-based rust preventive layer is formed on the Zn-Ni alloy layer, which is a surface treatment method for a copper foil for a printed circuit. 2. Cu, Cr, Ni, on the roughened surface of the copper foil,
The surface treatment method for a copper foil for a printed circuit according to claim 1, wherein a treat treatment for forming a single metal layer or an alloy layer of one or more selected from Fe, Co and Zn is performed. 3. A chromium oxide film and / or a chromium-based rust preventive layer formed by immersion chromate treatment or electrolytic chromate treatment.
The method for surface treatment of a copper foil for a printed circuit according to claim 1 or 2, which is formed from a mixed film of chromium oxide and zinc and / or zinc oxide by electrolytic zinc / chromium treatment.